Acetylene (useful for oxy-acetylene welding) is produced by reacting Calcium carbide (CaC2) with water.
Calcium carbide is generated by the carbothermic reduction of lime (CaO) at 2000C. Lime can be produced by reducing limestone (calcium carbonate) in a furnace at 900C-1000C. Once lime has been produced however, one does not need to continue to harvest more limestone to keep making acetylene. The reaction of calcium carbide with water produces acetylene and calcium hydroxide (Ca(OH)2). The hydroxide dissociates back into water and lime at 512C.
Carbon however, which is burned as acetylene, must be continually provided. Only the calcium is preserved.
thus the closed loop is:
Calcium hydroxide + 512C -> Calcium oxide (lime) + water
Calcium oxide + Carbon + 2000C -> Calcium carbide + Carbon Monoxide
Calcium carbide + water (room temp) -> Acetylene + calcium hydroxide.
Carbon may be provided from biomass (ie: charcoal). It would be useful to know what effect the presence of hydrogen has on the reaction in order to determine if wood gas, bio gas, and other easily attainable simple organic molecules could be used in place of pure carbon.
Halstead, P.E.; Moore, A.E. (1957). "The Thermal Dissociation Of Calcium Hydroxide". Journal of the Chemical Society 769: 3873. doi:10.1039/JR9570003873